A turbocharged engine offers performance benefits of a larger naturally aspirated engine. However, cold start emissions of a turbocharged engine may be greater than desired because a turbine within the turbocharger may extract heat energy from engine exhaust gases before the exhaust gases reach an after treatment device. Consequently, less exhaust energy reaches the exhaust after treatment device and the amount of time for the exhaust after treatment device to reach operating temperature increases. One way to increase the amount of exhaust energy that reaches the after treatment device is to retard engine spark timing and increase engine air mass flow rate. Nevertheless, the after treatment device may not reach operating temperature soon enough to pass stringent vehicle emission levels. Further, increasing spark retard and engine air mass flow rate increases fuel consumption and therefore may be undesirable.
The inventors herein have recognized the above-mentioned limitations and have developed an engine system, comprising: an engine; a turbocharger coupled to the engine, the turbocharger including a device for increasing and decreasing rotational resistance of the turbocharger; and a controller including non-transient instructions to adjust the rotational resistance of the turbocharger via the device in response to a temperature of an after treatment device being less than a threshold temperature.
By increasing the rotational resistance of a turbocharger turbine, it may be possible to reduce an amount of time for an after treatment device to reach an operating temperature. In particular, increasing rotational resistance of a turbocharger turbine can limit turbocharger rotation so that engine exhaust gases are exposed to less surface area within the turbocharger. Therefore, less exhaust energy may be imparted to the turbocharger so that more exhaust energy may be imparted to a catalyst positioned downstream of the turbocharger. The additional exhaust gas energy supplied to the catalyst may reduce engine emissions. In this way, engine emissions may be reduced without having to further retard spark timing and increase engine air flow.
The present description may provide several advantages. For example, the approach may reduce engine emissions during an engine cold start. Further, the approach may reduce fuel consumption by reducing catalyst light off time so that an amount of time the engine is operated less efficiently may be reduced. Further still, the approach may allow the engine to operate with greater combustion stability during engine starting so as to reduce rough engine idling.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.